1. Field of the Invention
The present invention relates to a method for attaching a cable for supplying power to a fluorescent tube, a method for manufacturing a surface illuminating device with the fluorescent tube, a fluorescent tube with cables, a surface illuminating device with the fluorescent tube and a liquid crystal display device having the surface illuminating device.
The present application claims priority of Japanese Patent Application No. 2000-333819 filed on Oct. 31, 2000.
2. Description of the Related Art
In recent years, in portable information devices such as notebook-type personal computers, it is required that they are made lightweight and thin. At the same time, as shown in FIG. 34, for example, in a notebook-type personal computer 101, an effort has been made to make a display area relatively large in size by making narrow, as much as possible, a width of a plaque edge portion 103 used to hold an edge portion of a liquid crystal display device 102 and being not contributing directly to a liquid crystal display.
Moreover, as shown in FIGS. 35 and 36, the liquid crystal display device 102 includes, for example, a transmissive-type TFT (Thin Film Transistor) liquid crystal panel 104, a backlight 105 used to apply illuminating light from its rear side and a front case 106 used as a holding frame to hold a main body of the liquid crystal display device 102. Here, the plaque edge portion 103 has to have a thickness of, for example, about 7 mm.
Moreover, the backlight 105, as shown in FIGS. 36 and 37, includes a fluorescent tube 108, a reflector 109 used to reflect light emitted from the fluorescent tube 108, a rear chassis 110 used as a holding frame on a rear side of the backlight 105, a light guiding plate 111 used to take in direct light from the fluorescent tube 108 or light reflected off the reflector 109 and to emit it as planar light, a reflecting sheet 112 disposed on the rear chassis 110 and used to reflect light emitted from the fluorescent tube 108 to a side of the light guiding plate 111, optical correction sheets 113, 113, . . . , made up of a plurality of pieces of prism sheets, diffusion sheets, or a like used to highly accurately correct variations in luminance and to improve uniformity in luminance, and a lamp cover 114.
The fluorescent tube 108, for example, in the case of the fluorescent tube to be used for a 14-inch type liquid crystal display device, is so formed that it has a shape of a narrow tube with a diameter of about 2 mm and a length of about 190 mm and that its both ends are sealed so that its inside portion is filled with mercury gas and inert gas in a sealed manner and that a pair of electrodes is sealed at both ends of the long cylindrical-shaped glass tube and that an ultraviolet ray reflecting layer and a phosphor layer are formed in an inside face of the glass tube. To each of the electrodes is connected each of lead conductors 115a and 115b. A pair of cables 116a and 116b for supplying power is connected to the fluorescent tube 108. Each of holding rubber caps 117a and 117b used to hold the fluorescent tube 108 is connected to each of ends of the fluorescent tube 108. The cables 116a and 116b are drawn out from a cable drawing-port 110a formed in the rear chassis 110.
On a side being opposite to the cable drawing-port 110a, as shown in FIGS. 38 and 39, the cable 116a is connected in a direction being approximately perpendicular to the fluorescent tube 108. That is, as shown in FIG. 39, the lead conductor 115a connected to the fluorescent tube 108 is bent at right angles. After having soldered the lead conductor 115a to a core wire 118a of the cable 116a, an end on a side of the cable 116a is covered with a thermal shrinkage tube 119 and fixed. Then, the L-shaped holding rubber cap 117a is attached to ends of the cable 116a and the fluorescent tube 108 and fixed. To protect connected portions, the holding rubber cap 117a is covered with another thermal shrinkage tube 120. As a material for the holding rubber cap 117a, a comparatively flexible material that can be easily attached is selected.
The methods to protect such the connected portions as described above by using the holding rubber cap is disclosed in, for example, Japanese Patent Application Laid-open Nos. Hei 7-281160 and Hei 7-281161.
In the disclosed method, as shown in FIG. 37 and FIG. 40, when the fluorescent tube 108 is embedded in the backlight 105, in order to prevent the connected portion in which the fluorescent tube 108 is connected to the cable 116a being subjected to stresses, the cable 116a is hung on a bump projection piece 110b formed on the rear chassis 110 and is then routed around to form a margin portion 121 and is finally drawn out from the cable drawing-port 110a. 
When the fluorescent tube 108 is embedded in the backlight 105, on a side being opposite to the cable drawing-port 110a of the cable 116a, for example, as shown in FIG. 41, a core wire 118b of the cable 116b is soldered, with a margin portion 122 formed by a tip portion of the core wire 118b being bent in a shape of a letter xe2x80x9cUxe2x80x9d, to the lead conductor 115b of the fluorescent tube 108 to be connected to each other and then a holding rubber cap 117b is covered to protect the connected portion.
However, the above conventional method has problems. That is, in the case of the method, in particular, in which the cable 116a is attached to an axis of the fluorescent tube 108 at right angles, to obtain mechanical strength at the connected portion, as described above, the cable 116a is hung on the bump projection piece 110b formed on the rear chassis 110 and is then routed around to form the margin portion 121 and is finally drawn out from the cable drawing-port 110a. As a result, a width of the corresponding plaque edge portion 103 becomes large. This causes a lowered ratio of a front area of the backlight 105, serving as a region in which light is emitted when the fluorescent tube 108 is embedded in the backlight 105, to its all surface area and a lowered ratio of a front area of the liquid crystal display device 102, serving as a liquid crystal displaying region when the backlight 105 is embedded in the liquid crystal display device 102, to its all surface area. For example, if a diameter of the cable 116b is about 1.6 mm and a thickness of the bump projection piece 110b is about 1 mm, to route the cable 116a, redundant space of at least about 3 mm along an axial direction of the fluorescent tube 108 has to be expended.
Moreover, when the cable 116a is attached to the axis of the fluorescent tube 108 at right angles, the lead conductor 115a is also bent at right angles. The holding rubber cap 117a is made up of flexible and soft materials. These factors cause the mechanical strength in the connected portions to become lower. If, therefore, a stress is applied on the connected portions in which the fluorescent tube 108 is connected to the cable 116a, a failure such as breaking of wires or a like readily occurs. Since the thermal shrinkage tubes 119 and 120 are used at the connected portion in which the fluorescent tube 108 is connected to the cable 116a, component counts become high and many man-hours and much time are required in assembling process of the connected portion.
Furthermore, there is another problem. That is, when the holding rubber cap 117a is used to position the reflector 109 to the fluorescent tube 108, the holding rubber cap 117a is easily deformed, which makes it difficult to perform exact positioning of the reflector 109 to the fluorescent tube 108. Because of this, for example, the reflector 109 is attached to a place being deviated from its originally expected position. This causes direct light from the fluorescent tube 108 or light reflected off the reflector 109 to be emitted in an unwanted direction, which causes degradation in luminance characteristics of the backlight 105 and to a decrease in its reliability.
In view of the above, it is an object of the present invention to provide a method for attaching cable to a fluorescent tube, a method of manufacturing a surface illuminating device, a fluorescent tube with cables, a surface illuminating device and a liquid crystal display device, which are capable of making small a width of a plaque edge portion by saving redundant space at a connected portion in which the fluorescent tube is connected to the cable.
It is another object of the present invention to provide the method for attaching the cable to the fluorescent tube, method of manufacturing the surface illuminating device, fluorescent tube with cables, surface illuminating device, and liquid crystal display device, which are capable of making low component counts of holding members such as a cable clamp or a like used to reinforce the connected portion in which the fluorescent tube is connected to the cable, of reducing the number of processes required for assembling these components, of enhancing mechanical strength of the connected portion in which the fluorescent tube is connected to the cable, thereby improving their reliability.
It is still another object of the present invention to provide the method for manufacturing the surface illuminating device, the surface illuminating device and the liquid crystal display device, which are capable of performing exact positioning among the fluorescent tube with cables, reflector, and light guiding plate, thereby improving their reliability.
According to a first aspect of the present invention, there is provided a method for attaching a cable to a fluorescent tube in which the cable for supplying power is to be attached to the fluorescent tube being used as an illuminant for a liquid crystal display device and which has a glass tube and a pair of electrodes each of which is mounted and sealed in each end of the glass tube, the method including:
a step of electrically connecting a core wire of the cable to each of terminals being connected to the electrodes and being exposed outside the glass tube; and
a step of housing a connected portion in which at least one of the terminals is connected to the core wire of the cable in a hollow of a mold having a hollow inside the mold and then injecting a resin into the hollow and having the resin hardened in the hollow and molding the connected portion to cover with a molded resin.
In the foregoing, a preferable mode is one wherein the step of the molding includes a step of housing at least one end portion of the glass tube and an end of an insulated portion of the cable on a side of the connected portion as well as the core wire in the hollow of the mold and then injecting, the resin into the hollow and having the resin hardened to cover with the molded resin.
Also, a preferable mode is one wherein, as the resin to be used, a material having heat resistance and electrical insulation is employed.
According to a second aspect of the present invention, there is provided a method for manufacturing a surface illuminating device which is used as an illuminating device for a liquid crystal display device having a fluorescent tube made up of a glass tube and a pair of electrodes each of which is mounted and sealed in each end of the glass tube, a reflector used to reflect light emitted from the fluorescent tube and a light guiding section used to guide direct light from the fluorescent tube or light reflected off the reflector in a direction approximately perpendicular to a light emitting face of the surface illuminating device, the method including:
a step of electrically connecting a core wire of a cable for supplying power to the fluorescent tube to each of terminals being exposed outside the glass tube being connected to the electrodes of the fluorescent tube;
a step of housing a connected portion in which at least one of the terminals is connected to the core wire of the cable in a hollow of a mold in which a convex-shaped portion or a concave-shaped portion is formed and then injecting a resin in the hollow and having the resin hardened in the hollow to cover the connected portion with a molded resin and, at the same time, of forming a concave-shaped portion or convex-shaped portion corresponding to the concave-shaped portion or convex-shaped portion and functioning as first and second positioning portions at predetermined places on the molded resin;
a step of attaching a reflector by having an end of the reflector come into contact with the first positioning portion, with the reflector being positioned to the fluorescent tube; and
a step of attaching a light guiding section by having an angled portion come into contact with the second positioning portion, with the light guiding section being positioned to the fluorescent tube.
According to a third aspect of the present invention, there is provided a fluorescent tube with cables to be used as an illuminant for a liquid crystal display device, including:
a glass tube;
a pair of electrodes each of which is mounted and sealed in each end of the glass tube;
a pair of terminals each being connected to each of the electrodes and being exposed outside the glass tube;
the cables for supplying power; and
wherein a core wire of the cable is electrically connected to each of the terminals and at least one connected portion is sealed with a hardened insulating resin thereat.
In the foregoing, a preferable mode is one wherein a resin-molded portion is formed by covering at least one end portion of the glass tube and an end of an insulated portion of the cable on a side of the connected portion as well as the core wire with a molded resin.
Also, a preferable mode is one wherein the resin-molded portion includes a first positioning portion with which an end of a reflector used to reflect light emitted from the fluorescent tube is put in contact for positioning when the reflector is attached to the fluorescent tube with the cables and a second positioning portion with which an angled portion of a light guiding section used to guide light emitted from the fluorescent tube to a predetermined direction is put in contact for positioning when the light guiding section is attached to the fluorescent tube with the cables.
Also, a preferable mode is one wherein the first positioning portion has a first step portion with which an end of the reflector is put in contact for positioning in a struck manner when the reflector is attached to the fluorescent tube with the cables and a second step portion with which an angled portion of a light guiding section is put in contact for positioning in a struck manner when the light guiding section is attached to the fluorescent tube with the cables.
According to a fourth aspect of the present invention, there is provided a surface illuminating device to be used as an illuminating device for a liquid crystal device including:
a fluorescent tube with cables to be used as an illuminant, having: a glass tube, a pair of electrodes each of which is sealed in each of ends of the glass tube, a pair of terminals each being connected to each of the electrodes and being exposed outside the glass tube, and the cables for supplying power; and
wherein a core wire of the cable is electrically connected to each of the terminals and at least one connected portion is sealed with a hardened insulating resin thereat;
a reflector used to reflect light emitted from the fluorescent tube; and
a light guiding section used to guide direct light from the fluorescent tube or light reflected off the reflector to a direction approximately perpendicular to a light emitting face of the surface illuminating device.
According to a fifth aspect of the present invention, there is provided a liquid crystal display device including:
a surface illuminating device described above; and
a liquid crystal panel.
With the above configurations, when the connected portion in which the fluorescent tube is connected to the cable is molded with the resin, a large thickness of the connected portion is not necessary if the thickness is large enough to maintain a predetermined mechanical strength of the connected portion. Moreover, routing of cables is not necessary. A cable clamp is not required. Space is not required redundantly at the connected portion. Therefore, it is possible to make narrower a plaque edge portion of the surface illuminating device and/or the liquid crystal display device using the fluorescent tube with the cables of the present invention.
Moreover, in the connected portion in which the fluorescent tube is connected to the cable, after the terminal of the fluorescent tube has been electrically connected to the core wire of the cable, the connected portion is molded with the resin and therefore the mechanical strength of the connected portion can be enhanced and the reliability can be improved.
Also, a thermal shrinkage tube, cable clamp or alike are not required in the connected portion and therefore it is possible to reduce counts of components and man-hours for assembly.
Also, work required to bend and route the cables for assembly is not necessary and therefore easiness of the assembly can be improved and replacement of the fluorescent tube can be made easily and within a short time.
Furthermore, the first and second positioning portions are formed in the resin-molded portion and therefore the exact and reliable positioning of the fluorescent tube with cables to the reflector or to the light guiding plate is made possible and yield is enhanced as a result.